Survival of Listeria monocytogenes in egg washwater

Abstract

The viability of Listeria monocytogenes strains Scott A, 78-34, and 81–861 in artificial egg washwater at different temperatures and pH values was determined. After a 4-h incubation, less than a 1-log decrease in viability of strains Scott A and 78-34 was found at 33°C with alkaline detergent (pH 8.0−10.5); however, up to a 3-log decrease in viable numbers was found in neutral pH controls lacking detergent. At 42°C, survival was generally poorer; complete loss of viability (>4-log decrease in viable numbers) was found within 2 h at neutral pH. Strain 81–861 was more sensitive to the test conditions than the other two strains. Viability of all strains was markedly lower in synthetic washwater at the lower pH values (pH 7–9) containing whole egg than washwater in which whole egg was omitted. The presence of whole egg appeared to have no effect on survival at pH 10.5. A limited survey of two egg wash facilities in Southeastern Ontario revealed Listeria innocua in environmental samples from both plants, and in washwater from one plant. These results suggest that Listeria spp. can survive normal commercial washwater conditions, and can be found in commercial egg wash plants.